Why have I been having nightmares for like the past 3 nights when normally I don't even dream?

Nightmares usually occur due to something in your subconcious (like you watched a horror film that scared you), stress, trauma or medication.

3 is the number of God. Is He giving you a message? We are living in the end times. Chaos will come shortly. Earthquakes and volcanoes will erupt. Do you know Jesus as savior. Cry out to Him for the salvation of your soul

http://www.edgarcayce.org/are/dreams.aspx?id=2484